Case hardening composition



chlorides and carbonates.

Patented May 22, 1951 2,553,855 CASE HARDENING 66 IsaacLaird-Newll,Wethersfield, Conn.

N0 Drawing. Application March 11, 1950, Serial No. 149,203

" 11 Claims.

This invention relates to a fusible salt bath for the treatment of ironor steel or ferrous alloys by a process generally known as carbur-izing.cementation or case hardening. More particularly the invention relatesto a novel composition and method for a case hardening treatment.

Case hardening baths have long been known and used to give a surfacehardness to iron and steel parts by the introduction of carbon andnitrogen into the surface of the metal. Such baths are usually composedof a cyanogen compound with or without an activating material toaccelerate or control the rate of case hardening. There is alsogenerally present such diluents as Cementation with carbon and nitrogenwill occur slowly when mixtures of sodium and potassium canides areused. By the addition of such activators as the alkaline earth metalsespecially calcium and barium in the form of chlorides and carbonatesthe rate of cementation is markedly increased and a higher proportion ofcarbon is introduced into the metal. There are objectionable features toeach of case hardening compound consists essentially of the sodium saltsof cyanide, cyanate, chloride and carbonate the bath is unstable andrequires frequent and large additions of cyanides. This bath isunreliable and does not give uniform depths of case.

Calcium compounds such as calcium oxide and calcium chloride arefrequently used as energizers or activators for cyanide baths, and whilecontrolled cementation is accomplished, the bath is hygroscopic andcorrosive to the work and furnace parts. The work is often coated withlime salts and acid treatment is required to clean the work.

Barium compounds are also successfully used to regulate the carburizingaction of salt baths but are characterized by the great diificultyencountered in cleaning the work after cement-ation. As with the calciumsalts, the compounds of barium are difiicultly soluble in water, andalkali cleaners and acid treatment is frequently necessary to clean themetal parts.

Other energizers such as fluorides are also used, but their effect isslight and results are often erratic.

I have found that a cyanide containing salt bath composition can beactivated or energized by the addition of an alkali metal fluosilicat'ealso known as silico fluoride. The resulting bath is not open to theobjections cited, and in addition has the following advantages: it iscompletely water soluble, and treated parts when quenched in water havea clean bright finish. The carburizing action is rapid and case depthsare obtained which are equivalent to those found when using barium andstrontium activated L-bath's.

The baths containing fluosilicates are very stable and little or nofuming or foaming is noted at operating temperatures. An added advantageis the low cost of the accelerator especially when compared to strontiumand barium compounds.

The amount of fiuosilicate salt necessary to produce effectiveactivation of a carburizing bath is low, and as small an amount as 2% issufficient in some cases. Satisfactory energizing is also obtained whenas much as 20% is used, but the bath becomes somewhat viscous and tendsto sludge when as much as this is used. The preferred compositionscontain from 4 to 12% of the fluosilicate salt.

The following examples will serve to further illustrate the invention:

Example 1 Iron wire having a diameter of 0.125 inch and a carbon content0.10 percent was treated at 1600 F. in a fused salt bath of thefollowing composition;

Parts by weight Sodium cyanide 20 Sodium chloride 44 Sodium carbonate 34Sodium fluosilicate 2 After an immersion time of one hour the depth ofcase was .012 inch and the surface was bright and file hard. The saltbath gave no evidence of sludge formation and fuming was slight.

Example 2 A steel rod having a carbon content of 0.012

percent was immersed in a fused salt bath of the following composition:

Parts by weight Sodium cyanide 20 Sodium chloride 43 Sodium carbonate30.99 Potassium fiuosilicate 6 Carbon .01

After an immersion time of one hour during which period the temperature:of the bath was maintained at 1650 F., the depth of case was found tobe 0.014 inch. The surface was bright and clean and file hard. Nosludging, frothing or foaming was noted.

Example 3 A case hardening bath was prepared by blending together thefollowing materials in powder form.

Parts by Weight Sodium cyanide 20 Sodium chloride 3'9 Sodium carbonate32 Sodium fiuosilicate 8 Carbon 1 The mixture was fused and maintainedat a temperature of 1600 F. In order to maintain the bath level fromloss due to dragout on the work and maintain activity which might havebeen lessened due to surface decomposition, a replenisher was addedregularly at the rate of 10 percent by weight of the bath per 8 hourday, the replenisher having the following proportions:

Parts by weight Sodium cyanide 40 Sodium chloride 39 Sodium carbonate 12Sodium fluosilicate 8 Carbon l 1 Steel rods, carbon 0.20%, manganese0.40%, phosphorus 0.04%, sulfur 0.04%, were treated in this bath andcyanide and case depths determina tions made.

Cyanide Concentration in Bath (Percent Sodium Cyanide) Days in OperationMicroscopic examinations for case depths showed the following averagefigures:

Depth of case Inches hr .010 1 hr .015 2 hrs .022

3 hrs .027 4 hrs .030

Example 4 A steel bolt having a carbon content of 015 percent wastreated in a fused salt bath of the following composition:

Parts by weight Sodium cyanide 40 Sodium cyanate 2 Sodium chloride 30Sodium carbonate 9 Potassium chloride Lithium fiuosilicate; 12

Carbon 2 The temperature was maintained at 1700 F. and after hr.immersion the case depth was found to be 0.011 inch.

Example 5 A salt bath of the following composition was fused andmaintained at a temperature of 1550 F.:

Parts by weight Sodium cyanide Sodium cyanate 5 Sodium carbonate 25Sodium chloride 34.5 Sodium fluosilicate 20 Carbon 0.5

The level of the bath in the pot was maintained by the regular additionof the following mixture,

making the addition at the rate of percent per hour.

Parts by weight Sodium cyanide '75 Sodium cyanate 4 Sodium carbonate .5Sodium fiuosilicate 15 Carbon 0.5

Steel rods having a carbon content of 0.15 percent were immersed in thisbath for 2 hours. A

- depth of case of 0.020 inch was produced.

Starting Replen- Salt isher Parts by Paris by weight weight SodiumCyanide l. 70-40 4075 Sodium Oyanate l 0-5 0-5 Sodium Chloride" 5-455-40 Sod um Carbonate. 5-35 5-20 Potassium Chloride.. 0-30 0-30 AlkaliMetal Fluosilicate. 2-20 220 Carbon 0-2 0-2 The higher the operatingtemperature, the faster the rate of cementation. Temperatures as high as1900 F. have been used without excessive frothing or foaming of thebath. And ternperatures as low as 1400 F. have been employed witheffective carburizingl What is claimed is:

l. A composition of matter for a case hardenin bath for iron, steel, andferrous alloys consisting of a mixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium chloride 5 to 45 Sodiumcarbonate 5 to 35 Alkali metal fiuosilicate 2 to 20 2. A composition ofmatter for a case hardening bath for iron, steel, and ferrous alloysconsisting of a mixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Alkali metalfluosilicate 2 to 20 3. A composition of matter for a case hardeningbath for iron, steel, and ferrous alloys consisting of a mixture of thefollowing ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Potassium chloride lessthan 30 Alkali metal fluosilicate 2 to 20 4. A composition of matter fora case hardening bath for iron, steel, and ferrous alloys consisting ofa mixture of the following ingredients:

Parts by weight Sodium cyanide to 40 Sodium chloride 5 to 45 Sodiumcarbonate 5 to 35 Potassium chloride less than 30 Alkali metalfluosilicate 2 to 5. A composition of matter for a case hardening bathfor iron, steel, and ferrous alloys consisting of a mixture of thefollowin ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium chloride 5 to 45 Sodiumcarbonate 5 to 35 Potassium chloride less than Carbon less than 2 Alkalimetal fiuosilicate 2 to 20 6. A composition of matter for a casehardening bath for iron, steel, and ferrous alloys consisting of amixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5Sodium chloride 5 to 45 Sodium carbonate 5 to Carbon less than 2 Alkalimetal fiuosilicate 2 to 20 '7. A composition of matter for a casehardening bath for iron, steel, and ferrous alloys consisting of amixture of the following ingredients:

Parts by Weight Sodium cyanide 10 to 40 Sodium chloride 5 to Sodiumcarbonate 5 to 35 Carbon less than 2 Alkali metal fiuosilicate 2 to 208. A composition of matter for a case hardening bath for iron, steel,and ferrous alloys consisting of a mixture of the followin ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Carbon less than 2Sodium fiuosilicate 2 to 20 9. A composition of matter for a casehardening bath for iron, steel, and ferrous alloys consisting of amixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Carbon less than 2Potassium fiuosilicate 2 to 20 10. A composition of matter for a casehardening bath for iron, steel, and ferrous alloys consisting of amixture of the following ingredients;

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Carbon less than 2Lithium fiuosilicate 2 to 20 11. A composition of matter for a casehardening bath for iron, steel, and ferrous alloys consisting of amixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate Less than 5Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Potassium chloride Lessthan 30 Carbon Less than 2 Alkali metal fluosilicate 2 to 20 ISAAC LAIRDNEWELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,804,454 Beck May 12, 1931 OTHERREFERENCES Molten Salt Baths, page '7, published by Du Pont de Nemours &Co. Inc., 1946.

1. A COMPOSITION OF MATTER FOR A CASE HARDENING BATH FOR IRON, STEEL,AND FERROUS ALLOYS CONSISTING OF A MIXTURE OF THE FOLLOWING INGREDIENTS: